Chest X-ray assessment of heart size and chamber enlargement
THE CONTEXT
Chest radiography helps assess cardiac size and shape, pulmonary blood vessels and lung fields. Projection and chamber-specific silhouette changes affect interpretation.
Projection
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A postero-anterior (PA) projection taken in full inspiration provides the most information.
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An anteroposterior (AP) projection can be obtained when patient movement is restricted, but it magnifies the cardiac silhouette.
Cardiomegaly and its limitations
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Estimate overall heart size by comparing the maximum cardiac width with the maximum internal transverse diameter of the thoracic cavity. A ratio greater than 0.5 indicates cardiomegaly.
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An enlarged cardiac silhouette may result from chamber dilatation, especially left ventricular dilatation, or pericardial effusion. A mediastinal mass or pectus excavatum may also account for the appearance.
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Cardiomegaly is not a sensitive indicator of left ventricular systolic dysfunction: many patients with poor left ventricular function have a normal cardiothoracic ratio.
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Cardiomegaly is also not specific for left ventricular systolic dysfunction: many patients with radiographic cardiomegaly have normal echocardiograms.
Chamber-specific silhouette changes
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Left atrial dilatation produces prominence of the left atrial appendage and a straight left heart border, a double cardiac shadow to the right of the sternum, and widening of the carinal angle as the left main bronchus is pushed upwards.
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Right atrial enlargement projects from the right heart border towards the right lower lung field.
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Left ventricular dilatation causes prominence of the left heart border and enlargement of the cardiac silhouette. Left ventricular hypertrophy produces rounding of the left heart border.
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Right ventricular dilatation increases heart size, displaces the apex upwards and straightens the left heart border.
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The illustrated patient with mitral stenosis and regurgitation has left atrial enlargement and a prominent pulmonary artery trunk.